The long-term objectives of this project are to understand the roles of signal transduction pathways of the receptor tyrosine kinases, Tie1 and Tie2, in human pathological blood vessel formation and to develop novel therapeutics to prevent and/or cure diseases in which blood vessel formation play a role. Tie 1 and Tie2 form a novel family of vascular endothelial cell-specific receptor tyrosine kinases and they play critical roles in blood vessel formation during development. Their important functions during human pathological blood vessel growth have also been implicated. We propose the following four specific aims to accomplish our long-term goals: First, we will determine the spacial and temporal expression patterns of Tiel and Tie2 in human atherosclerotic vascular disease. Second, we will test the hypothesis that Tie1 and Tie2 have important roles in relatively mature blood vessels. This will be studied by genetically manipulating the mice so that either the Tie1 or Tie2 gene is mutated only in late embryonic stages and/or postnatal mice. Third, we will determine the roles of cytoplasmic tyrosine residues of both Tie1 and Tie2. The roles of potentially important tyrosine residues in Tie1 and Tie2 will be studied in vivo by introducing point mutations to these tyrosine residues in transgenic mice. Fourth, we will test the hypothesis that p120-GAP and p190 play critical roles in blood vessel formation in vivo. Putative dominant-negative mutant forms of p120-GAP and p190 will be over-expressed under the control of endothelial cell-specific promoters to interfere with the function of these genes, specifically in endothelial cells. These approaches will provide us with the initial step towards designing ways to manipulate the signalling pathways downstream from the Tiel and Tie2 tyrosine kinases in human vascular diseases.